Beater saturation of asbestos fibers



United States Patent BEATER SATURATION OF ASBESTOS FIBERS David A.Feigley, J12, Lancaster Township, Lancaster County, Pa., assignor toArmstrong Cork Company, Lancaster, Pa., a corporation of Pennsylvania NoDrawing. Application July 22, 1953, Serial No. 369,724

6 Claims. (Cl. 92--21) This invention relates to the preparation ofsaturated asbestos tfiber sheet materials. More particularly, theinvention relates to a process of preparing such products in which therubber content of a rubber latex is deposited upon the fibers while insuspension, such as in a conventional papermaking beater, and thereafterforming the resulting slurry of coated fibers into a sheet.

Rubber-bonded asbestos fiber sheet material has been prepared by anumber of methods, including one known as the beater saturation process,which includes depositing the solids content of a rubber latex upon thefibers while in a slurry, and thereafter forming a sheet from the coatedfibers by means of conventional papermaking techniques. This processoffers numerous advantages, as improved physical properties such as hightensile strength and the like may be obtained. However, there have beennumerous difficulties involved in the production of an asbestos sheet bythe beater saturation process, inasmuch as the asbestos fibers differsignificantly from other papermaking fibers, such as wool or cellulose.Generally speaking, beater saturation methods which gave uniformly goodresults with cellulose fibers failed to work well upon asbestos fibers.It was not possible to obtain uniform distribution of binder solids uponthe asbestos fibers because of poor precipitation of the binder.

I have found that the poor results obtained when attempts are made tocoagulate rubber or other binder material upon asbestos fibers suspendedin Water are due to the presence in the water of substantial amounts ofmetallic ions derived from the asbestos. Asbestos fibers contributepolyvalent metal ions to the aqueous slurry and these ions cause animmediate partial precipitation when the rubber latex is added andbefore good mixing can be obtained. As a result of this partialprecipitation, the finished sheet is characterized by poor distributionof the rubber binder. The effect upon the stability of the rubber latexshould become apparent upon an analysis of a typical Canadian asbestosfiber material. The composition of a typical Canadian asbestos analyzesas follows:

Percent SiOz 38.7 Fe203 3.07 MgO 41.93 A1203 0.66 FeO 2.05 H2O 13.53

I have further found that rubber bonded asbestos sheet materialcharacterized by uniform distribution of the rubber over the fibers maybe produced by a beater saturation process in which certain sequesteringor chelating agents are added to the slurry prior to the addition of thesynthetic rubber latex which is to be coagulated to form the binder ofthe asbestos sheet material. These sequestering agents apparently form anon-ionizing complex with the metallic ion-s present in the water andthereby prevent partial precipitation of binder solids before thedesired mixing can be obtained.

1 have obtained particularly advantageous results in the practice of myinvention by the addition to the slurry of asbestos fibers, prior tolatex addition, of selected watersoluble polycarboxylic acids and/orwater-soluble salts thereof. These polycarboxylic acids aretricarboxylic acids such as citric acid and tetracarboxylic acids suchas ethylene diamine tetra-acetic acid.

As indicated above, water-soluble salts of such acids may be employed inthe practice of my invention. Examples of such water-soluble salts arethe alkali metal salts such as sodium, potassium, and lithium of theacid set forth above. Generally speaking, I have obtained particularlyadvantageous results when the sodium salts of the selectedpolycarboxylic acids are employed. The sodium salts maintain the pH ofthe water slurry neutral or slightly alkaline and thus enhance itscompatability with anionic latices normally employed in the beatersaturation process.

The rubberlike binder employed in the practice of my invention may beany of a number of synthetic rubbers used in the practice ofconventional beater saturation methods. Typical of these syntheticrubbers are the products known as GR-S, which is a copolymer ofbutadiene and styrene containing about 50% to about 70% butad'iene;Hycar, which is a copolymer of butadiene and acrylonitrile containingabout 60% to about butadiene; and neoprene, which is a polymer of2-chloro-butadiene 1,3, generally referred to as chloroprene. Ifdesired, homopolymers of butadiene may be employed, as well ashomopolymers and/or copolymers of butadiene homologues, such asisoprene. These materials can be generically designated as syntheticrubbers and more speoifically designated .as rubberlike polymers ofbutadiene, isoprene, and chloroprene, and rubberlike copolymers ofbutadiene or isoprene with copolymeriz-able vinyl compounds such asstyrene and acrylonitrile. As is well known in beater saturationmethods, these synthetic rubbers are added to the slurry in the form ofa latex. These latices normally contain about 25% to about 40% solids.Such latices contain additional compounding ingredients such .asstabilizers and the like which are well known to the art and which formno part of this invention.

After the slurry has been treated with the selected polycarboxylic acidor water-soluble salt thereof, a synthetic rubber latex is then addedand the mass is slowly agitated. As the slurry is agitated, the rubbercontent of the latex coagulates and evenly deposits upon the asbestosfibers. The resulting slurry of coated fibers is then formed into asheet on conventional papermaking equipment, such as a F-ourdrinier wireor a cylinder machine.

In order to obtain most advantageous results, I have found that thequantity of selected polycarboxylic acid or water-soluble salt thereofshould be between about .8 pound and about 1.2 pounds per 900 gallons ofwater. In other words, the selected polycarboxylic acid or salt thereofis used in amounts equivalent to 107 to parts per million of water byweight. Unless the minimum amount of agent is employed, the coagulationof the latex may result in a knotty, lumpy precipitate, whereas whenmore than the maximum amount is utilized, the

slurry is quite slow draining.

J. in order to n tue fully understand my invention, reference may be hadto the following specific examples:

EXAMPLE I" 90 pounds of asbestos fibers were added to 990 gallons ofwater. 1 pound of sodium citrate was added as a granular solid and theslurry agitatedto insure co mplete solution of the citrate anditssubsequent reaction with Mg and otherpolyvalent ions derived from theasbestos fibers' 51 pounds of l-Iycar 1561 latex tbuttldlielfiac'rylonitrile" copolyme1- 40% solids) were theiua dded withagitation. The solids content of the latex slowly and evenly depositedupon the asb estos' fibers. 'Ihe resulting slurry" of coated fibers wasthen formed into a sheeton'a' Fourdrinier wire. 1

90 pounds of asbestos fibers were suspended in 909 gallons 'o'fwater. .8pound of the sodium salt of ethylene diamine tetra-acetic acid was addedas a granulansolid and the slurry agitated to insure complete solutionof the tetra-acetic acid'salt and its subsequent reaction with Mg andother .p'olyvalent ions derived from the asbestos fibers. 51 pounds ofHycar 156 l latex (butadieneacrylonitrile copolymer-40% solids) werethen added with agitation. The solids content ofthe latex slowly andevenly deposited upon the asbestos fibers. The res'ulting slurry ofcoated fibers was then formed into a sheet on a'Fourdrinier wire. 7

In the above'examples the sequestering agent is added to the slurry as agranular solid. However, it is within the scope of my invention todissolve the sequestering agents in water and add the resulting solutionto the slurry of asbestos fiber sat the appropriate time.

The rubber-bonded asbestos sheets of my invention may be used in a widevariety of applications. However, they are particularly suited fortheform ation of high quality gasket material. Beater-saturated asbestossheets made in accordance with my invention are characterized byimproved tensile strengths as indicated wine renew ing table:

Table A Tensile Tensile Strength Before Hour at Heat, it/sq. 300? 15.,

t -#/sq. n1.

entrain o nt oi a 750 =3, 55o t ende ed Shee Q 3;- I

Whil hare s s b d m i vent on with particular reference to thedeposition ot 'binder, from synthetic. rubber latices, it should beunderstood that the process is applicable wherever a binder suspensionis aifected by the presence of metal ions derived from asbestos. Thus,the binder suspension may be a latex containing butadienerstyrene resinsand/or polyvinyl chloride resins, asphalt emulsions, and/or mixtures ofsuch suspensions with each other or with the rubber latices describedabove.

Bymeans of my invention, I may deposit up -;to 1 00%, by weight ofbinder on the weight. of the asbestos fibers.

I claim:

'1. A method of making a beater-saturated asbestos sheet comprisingforming a slurry of asbestos fibers in water; "adding a compound of thegroup consisting of water-soluble tricarboxylic acids, water-solubletetracarboxylic acids, and water-soluble salts thereof to form anonionizing complex with dissolved metallic ions derived from theasbestos fibers; adding a synthetic rubber latex to the resulting slurrywhile agitating said slurry whereby .the solids content of the bindersuspension is ve ly depos ed .up nsaid fi d rm the sult ing slurry .ofcoated fibers into a sheet.

2. A method of rnalging a rubber-bonded asbestos sheet comprisingforming a slurry of asbestos fibers in water; adding a cornpound of thegroup consisting of watersoluble tricarboxylic acids, water-solubletetracarboxylic acids, and water soluble salts thereof to said slurry toform a nonionizing complex with dissolved metallic ions derived fromsaid asbestos fibers; adding a latex of a synthetic rubber of the groupconsisting of rubberlike polymers of butadiene, rubberlikc polymers.ot-isoprene, ruhberlike polymers of chlonoprene, 'rubberlike copolym n.Q b t dic e with p l m fl v yl compo nds andjrubberlike copolyrners ofisoprene with v tipolym erizable vinyl compounds while agitating saidslurry whereby the solids content of said latex is evenly deposited uponsai fiber and m n th resulting lur o coat bers i t "a S et- 1A method ofmaking a rubber-bonded asbestos sheet comprising forming a slurry ofasbestos fibers in water; adding 107 to parts per million by weight ofsaid water of a compound of the group consisting of water.- s olu'bie'tricarboxylic acids, water-soluble tetracarbpxylic acids, andwaterr'soluble salts thereof to form a nonionizing complex withdissolved metallic ions derived from said asbdStfls fibcm; adding asynthetic rubber latex to said slurry while agitating whereby the rubbercontent of said la x is evenly deposited upon said fibers; and formingthe resulting slurry of coated fibers into a she t.

4. h ethod of making a rubber-bonded asbestos sheet comprising forming aslurry of asbestos fibers in water, adding 107 to 160 parts per millionby Weight of said water of sodium citrate to said slurry to form anonionizing complex with dissolved metallic ions derived from saidasbestos fibers; adding a synthetic rubber latex to the reg slurry whileagitating whereby the solids content .X p s e s el s i fi d farmin gslurry of coated fibers into a sheet.

' hod of'n aking a rubber-bonded asbestos. shect ril m' '.f m a Slurryof asb s o fi in. te m .07 t9. 169 P rt P r m lliq by Weight Qf a l 'i stric a to id Slurry to f r a n' t sniz n complex with dissolved metaliicions derived from said asbestos fibers; adding a synthetic rubber latexto the rel pg 'lur y' While, ta ing whe b the o ds ontent of an la er id po ited p a fi e s; n formin tl 1'e. r'esultin g slurry of coatedfibers into a sheet,

A; A hod of making a rubber-bonded asbestos sheet comprising forming aslurry of asbestos fibers in water; adding 107 to 160 parts per millionby weight of said water of sodium salt of ethylene diamine tetraaceticacid to slurry to form a nonionizing complex with dissolved metallicions derived from said asbestos fibers; addingisy'n'thetic rubber latexto the resulting slurry while egi ta ng whereby the solids content ofsaid latex is deposited upon said fibers; and forming the resultingslurry of coated fibers into a sheet.

R fe ee l t-ed in the l f i pa n urn-ran STATES PATENTS 1,502,686Sc-hidrowitz July 29, 1924 1.,90f7;,6-l6 Tucker May 6, 1933 1,956,053 'Ier Apr.'2 4, 1934 2,133,693; Greider et a1. V oer. l8, 1938;

(Other-references on following page) Neubert et a1 Dec. 27, 1949 NovakJan. 20, 1953 Wilson et a1 Feb. 17, 1953 FOREIGN PATENTS France Jan. 6,1937 OTHER REFERENCES Martell, Chemistry of the Metal Chelate Compounds,pub. by Prentice Hall, N. Y. 1952, pages 516, 540, 541,

5 545 and 546. (Copy in Div. 67.)

1. A METHOD OF MAKING A BEATER-SATURATED ASBESTOS SHEET COMPRISINGFORMING A SLURRY OF ASBESTOS FIBERS IN WATER; ADDING A COMPOUND OF THEGROUP CONSISTING OF WATER-SOLUBLE TRICARBOXYLIC ACIDS, WATER-SOLUBLETETRACARBOXYLIC ACIDS, AND WATER-SOLUBLE SALTS THEREOF TO FORM ANONIONIZING COMPLES WITH DISSOLVED METALLIC IONS DERIVED FROM THEASBESTOS FIBERS; ADDING A SYNTHETIC RUBBER LATEX TO THE RESULTING SLURRYWHILE AGITATING SAID SLURRY WHEREBY THE SOLIDS CONTENT OF THE BINDERSUSPENSION IS EVENLY DISPOSITED UPON SAID FIBERS; AND FORMING THERESULTING SLURRY OF COATING FIBERS INTO A SHEET.